ECOHYDROLOGICAL CHANGES IN THE MURRAY-DARLING BASIN .1. THE NUMBER OF TREES CLEARED OVER 2 CENTURIES

1. The Murray-Darling Basin occupies over 1 million km2 of south-eastern Australia. Since European settlement 200 years ago, massive tree clearing and disturbance to other native vegetation types has resulted in increases in dryland and stream salinity. 2. An attempt is made to estimate the number of trees cleared from the Basin. This information is useful for making decisions on broad policy and revegetation prescriptions. 3. Structural classes for pre-European and present-day vegetation were previously mapped at the 1:5 million scale. Digital versions of these maps were used to quantify the original and present-day areas for each class. The number of trees per class was established by field sampling. Information on areal extent and number of trees per class was then used to estimate total number of trees per class. 4. The pre-European total number of trees was estimated as 20-23 x 10(9), and present-day numbers around 8 x 10(9). 5. The replanting of some 12-15 x 10(9) trees over a wide area is unlikely due to high cost and current land uses. Strategic planting based on significant impacts on local and regional water balances seems the most useful approach.